Re: Last Call: draft-klensin-rfc2821bis

It might be the case that it's useful for an MTA to have an option to 
skip MX lookup for specific destinations because of DNS brokenness at 
those destinations.  But this seems to me to be outside of the scope of 
the standard.  Skipping MX lookup is not acceptable as a general 
practice, nor is it something we want to encourage.

In general, it's always been acceptable to configure an MTA to handle 
mail in some special-case way for specific domains where there was 
specific knowledge such that the special-case handling made sense for 
those domains.  The MX-then-A lookup is what you should do in the 
absence of any such knowledge.

Ned Freed wrote:
> 
>> --On Tuesday, 25 March, 2008 23:18 -0400 Keith Moore
>> <moore@network-heretics.com> wrote:
> 
>>>> You know, that's a very interesting point. One of more common
>>>> configuration variations we see is to disable MX lookups and
>>>> just use address records.
>>> how does anyone expect that to work across administrative
>>> domains?
> 
>> Sorry, I'm now completely confused.  Maybe it has just been a
>> long day, but...
> 
>> Ned, by "disable MX lookups", do you mean "don't put MX records
>> into the DNS zone and therefore force a fallback to the address
>> records" or "ignore the requirement of the standard that
>> requires using MX records if they are there"?
> 
> I'm talking about having the ability to disable DNS MX lookups entirely
> and fall back to address information.
> 
>> If the latter,
>> the behavior, however useful (or not) is, IMO, so far outside
>> the standard that it is irrelevant to any discussion about how
>> DNS records are used in a standard way.
> 
> I'm sorry, but i don't see it that way. I was close to convinced that this sort
> of fallback behavior was no longer useful under any circumstances until Bill
> reminded me that's not the case.
> 
> 				Ned
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